A wireless network is typically divided into a plurality of zones covering a plurality of cells. Each zone is served by a Mobile Switching Center (MSC) and each cell within the region is served by a base station. A wireless mobile station communicates with other stations (wireless or wired) via the base station covering the cell in which the station is located. When a mobile station leaves one zone and enters another zone, then it will begin to receive the identity of a base station within the other zone. At that point, the mobile station will note a change in the identity of the zone that it has been tracking, and, therefore, concludes that it has entered another zone. The mobile station announces its presence in the latter zone by "re-registering" with the latter base station.
Managing the tracking of a mobile station as it "roams" from one zone to another zone is an important aspect of wireless networking. One such prior managing scheme uses a Home Location Register (HLR) specified by the so-called IS-41 standard to store the identity of the current (or last known) region covering the zone in which a wireless mobile is located. It also uses a so-called Visitor Location Register (VLR) at the region level to store the identity of the zone that the mobile is currently located. If the wireless mobile moves from a first zone to a second zone, then the mobile station re-registers with a base station in the second zone, as discussed above. The latter base station then notifies its associated MSC that the location for the mobile has changed. The MSC, in turn, updates the contents of the associated VLR to reflect the mobile's new location. If the mobile then moves to another zone within another region, then the tracking of the mobile proceeds similarly in the other region. However, in this instance, the VLR associated with the other region will note that the mobile represents a new tracking entry and, therefore, notifies the HLR associated with the mobile that the mobile is now in a region served by the latter VLR. That VLR also notifies the former VLR to cancel its tracking of the mobile. Thus, in this two-level hierarchical scheme the HLR tracks which VLR a mobile is in, and the VLR tracks which of its zones (and thus the MSC) is covering the mobile. (Note that the area covered by VLR is referred to as a "region".)
Thus, if a telephone call is placed to a mobile from a distant region, then the MSC at the distant region sends a query to the HLR to obtain the location of the called mobile. The HLR, in turn, identifies the VLR now serving the mobile based on the contents of the home register associated with the mobile. The HLR then notifies the identified VLR via the associated network that a call is to be routed to the mobile. The identified VLR similarly notifies the MSC serving the zone in which the mobile is located. That MSC then returns a so-called Temporary Local Dialing Number (TLDN) that is to be used as the mobile identification Number in the routing of the call. The VLR also uses the TLDN to identify the mobile. The VLR then sends the TLDN to the HLR, which then forwards the TLDN to the MSC handling the call.
The locating of the mobile thus involves the sending of a signaling message from the HLR to the VLR, the re-sending of the signaling message from the latter VLR to the MSC currently tracking the mobile, a return signaling message from that MSC to its VLR, the re-sending of the return message from that VLR to the HLR, and the re-sending of the return message from the HLR to the local MSC handling the call. The latter MSC then routes the call to the distant MSC based on the TLDN assigned to the call.
An example of the mobile location procedure specified by the IS-41 standard is illustrated in FIG. 1A. Specifically, in response to an incoming call directed to a particular mobile, either the switch that received the incoming call from a calling party (originating switch) or the home switch associated with the called mobile sends a so-called Location Request (LOCREQ) message to the HLR supporting the called mobile. That HLR, in turn, sends a so-called Route Request (ROUTEREQ) message to the VLR from which it received the last registration message for the called mobile. That VLR in turn sends the ROUTEREQ message to the MSC. The MSC, in response to receipt of the ROUTEREQ message, assigns a TLDN (i.e., Temporary Location Directory Number) to the called mobile and returns this value in its response. The routing of the connection through the network is then done using the assigned TLDN identifying the far end MSC associated with the called mobile. When a conventional call setup message reaches the far end MSC, then that MSC pages its associated base stations as a way of locating the base station serving the cell in which the called mobile is located. (Note that the VLRs and MSCs need not exchange such messages if they are collocated with one another.)
It may be appreciated that the foregoing locating scheme is complex and uses an appreciable amount of processing time to set up a call.
Another proposed tracking scheme (referred to as "flat tracking") uses one level of tracking when a mobile is located within its "home" region/network and uses two levels when the mobile is located within another region/network. Specifically, when a mobile is in its home region, then it is tracked directly by the HLR, and when it is in another region, then the HLR is used to track the VLR of the other region. The latter VLR, in turn, tracks the location of the mobile. Also, for the latter case, the VLR assigns the TDLN, rather than the MSC. FIGS. 1B and 2 respectively illustrate in a logical manner the signaling that occurs for the one level and two level cases. For the one level case, HLR 5-1 tracks the locations of all mobiles assigned to the associated "home" network. In that case, if a user at wireless mobile m.sub.2 places a call to a user associated with wireless mobile m.sub.1, then, responsive to the call, MSC 5-3 sends a locate message to HLR 5-1, which has been tracking the mobiles that are within their home location served by HLR 5-1. Since that applies to wireless mobile m.sub.1, then HLR 5-1 returns to MSC 5-3 a TLDN that is to be used in setting up the call to MSC 5-2. MSC 5-3, in turn, forwards a call set-up message containing, inter alia, the supplied TLDN and Mobile Identification Number (MIN) associated with wireless mobile m.sub.1 to MSC 5-2.
If, on the other hand, wireless mobile m.sub.1 "roams" to a remote region as shown in FIG. 2, then its location is tracked in the manner discussed above, i.e., via VLR 5-4. However, in the improved scheme of FIG. 2, if wireless mobile m.sub.2 places a call to m.sub.1, then the TLDN is provided by VLR 5-4 (which covers the region in which wireless mobile m.sub.1 is currently located) rather than MSC 5-5 currently serving wireless mobile m.sub.1 at the remote location.
In addition, VLR 5-4 assigns a TLDN based on the MSC at which the mobile is currently located. For example, if the area code plus exchange code for MSC 5-5 is, e.g., 415-949, then VLR 5-4 assigns a TDLN of 415-949-0000 and returns that number to HLR 5-2, where "0000" identifies a call to a mobile terminal. Thus, by combining the function of a one-level tracking scheme for mobiles located in their home regions, and the assigning of a TLDN by an HLR or VLR, rather than an MSC, the location and call set-up procedures for home mobiles only involves a one hop message exchange instead of a three hop exchange, as would be the case in an IS-41 network (FIG. 1A).
Another proposed hierarchical location management scheme, which supposedly reduces long-distance signaling for tracking mobiles and location management is shown in FIG. 3. The node at the highest level is arbitrarily designated "earth", which is followed by a next tier of nodes representing respective countries. For example, the first node in the latter tier represents the U. S., which is followed by still another tier of nodes representing states or regions within the identified country, e.g., node 1 representing Florida. The latter tier of nodes serve mobiles, m, and other endpoints, such as mobile data terminals, E. Thus, a node tracks the location of the mobiles that are below it in the hierarchy. The earth node tracks the locations of mobiles covered by the level of nodes just below it, i.e., the country nodes. The latter nodes similarly track the locations of mobiles covered by their associated nodes positioned at a next lower level, e.g., the state nodes, and so on. If a wireless mobile m.sub.3, whose home node is node 1, moves to node P-Q then the system, in response to the move (which move is announced as a result of wireless mobile m.sub.3 re-registering with node P-Q) sets up a chain of pointers as shown in FIG. 3 from the home node 1 to node P-Q. If another mobile or endpoint, e.g., endpoint E.sub.n, then places a call to wireless mobile m.sub.3, node P sends a call set- up message to node Y in the direction of the home node (node 1) associated with wireless mobile m.sub.3. Since node Y has a pointer/entry noting that node P-Q is the location of wireless mobile m.sub.3 then the upward migration of the message stops at node Y, which then sets up a connection to node P-Q. The chain of pointers thus obviates the need to perform long distance signaling between one end node, e.g., node P, and a home node, e.g., node 1, to establish a connection to a mobile that has moved from its home location to a remote location. Moreover, if wireless mobile m.sub.3 continues to move, for example, moves to node P, then the mobile tracking updates generated as a result of such moves propagate up to node Y only. In that instance, only node Y changes its pointer from node P-Q to node P for wireless mobile m.sub.3.
It is apparent from the foregoing schemes that the prior art strives to reduce the amount of time and cost expended in tracking the location of a wireless mobile, e.g., a wireless data terminal, as well as the time and cost expended in setting up a call to a wireless mobile.